Present means for the release of pressure in sphygmomanometer cuffs conventionally take the form of a manually operable pressure release valve located in the tubing line between the "squeeze" bulb and the cuff at a point therealong just in advance of said squeeze bulb. Unfortunately, such valves are subject to wear and when worn result in jerky cuff deflation, making blood pressure estimations both difficult and inaccurate. Indeed, as many as 20% of a hospital's sphygmomanometers may be so disabled and/or out at one time for repair of the worn valve, which fact points to the need of a pressure release means which is not subject to wear and which at the same time makes deflation of the pneumatic cuff possible of attainment.
To assist in an appreciation of this need, the following brief description of the instruments now in use for and how blood pressure is taken therewith follows;
These instruments consists of a wrap-around cuff incorporating a pneumatically inflatable bag. Two tubes are connected to said inflatable bag, one extending to a squeeze bulb used for inflation of said bag, and the other extending to a manometer, i.e. a pressure indicating device which may consists of a mercury-column type manometer or a spring-type manometer.
The aforesaid squeeze bulb, which is provided at its opposite ends with a one-way air inlet valve and with a one-way outlet valve, respectively, is normally maintained distened by virtue of its configuration and the form-sustaining material, usually rubber, from which it is fashioned. However when squeezed, air pressure within the bulb is increased to a degree closing its one-way air inlet valve and opening its one-way outlet valve thereby forcing air into the tubing line extending to the pneumatic cuff and when squeeze pressure on the bulb is released, the bulb reforms, air being thereby drawn into its interior via the one-way air inlet valve.
Conventionally, air pressure in the tubing line and in the bag component of the pneumatic cuff may be lowered by means of the manually operable screw-type valve which is subject to wear, as previously noted.
In taking ones blood pressure by use of an instrument as foresaid, the pneumatic cuff is wrapped around the patient's arm (between elbow and shoulder) and air is pumped into the inflatable bag component thereof by squeeze pressure applied to the bulb, thereby raising the mercury column to 200-250 mm (such assuming a mercury manometer is used), with the result that the artery is compressed to a degree that blood flow beyond the cuff does not occur and the distal portion of the artery is collapsed.
The manually operable screw-valve which up to this point of the procedure has been closed to prevent the escape of air is now opened slightly to allow pressure in cuff to fall.
When the pressure in the cuff is lowered to a certain point-- the pressure in the artery resulting from contraction of the heart begins to cause "squirts" of blood to escape under the cuff to the distal collapsed artery. This produces a sound with each squirt which is heard with a stethoscope placed over the collapsed artery, such sounds being known as Korotcoff sounds, named for the physician who first described them.
At the pressure point at which these sounds come through with each heart beat -- the systalic blood pressure, i.e., the highest pressure which results from contraction of the heart, is recorded.
Even when the heart is at rest, however, pressure is maintained in the arteries. Such pressure, termed the diastalic pressure, is determined as follows;
Air pressure in the inflatable bag is gradually reduced by allowing air to escape via the screw valve. During this release of pressure, blood continues to squirt from under the cuff into the distal artery producing Korotcoff sounds. When, however, pressure is lowered sufficiently, blood-flow beneath the cuff becomes continuous and the Korotcoff sounds become muffled or disappear, the pressure at this point as registered on the manometer being the patient's diastalic pressure.
From the foregoing, the importance and indeed the crying need of and for a means for releasing the pressure in sphygmomanometer cuffs smoothly and with uniformly predictable results not possible of attainment with presently used pressure release valves employed for this purpose because they are subject to wear and/or being otherwise disabled, becomes apparent, and it is a major object of the present invention to provide pressure release means of simple construction which is capable of effecting smooth deflation of said cuffs as needed, and in addition fulfills the additional objectives of inexpensive manufacture, longer useful life, simplicity of operation and ability to be packed in a smaller case than sphygmomanometers equipped with a screw valve in the tubing line to the cuffs as heretofore conventionally used for deflating said cuffs as needed.